1. Field of the Invention
This invention relates to devices employing silicon compounds and in particular to devices employing silicon compounds with Si--Si bonds.
2. Art Background
Silicon compounds are utilized for a variety of applications. Silicon dioxide is used as a common dielectric for a variety of devices including those having optical and/or electronic components. Other silicon compounds have also been suggested for use in the fabrication of such devices. In particular, polysilanes (linear polymers generically represented as [R.sub.1 R.sub.2 Si].sub.n with each silicon atom bound to two other silicon atoms and to two organic substituents R.sub.1 and R.sub.2) have been synthesized. (See West in Journal of Organometallic Chemistry, 1986, page 300 to 327 and references cited therein.) These polymers, when irradiated with electromagnetic radiation, undergo degradation reactions to produce fragments that are significantly more soluble than the polymer. Thus, the materials have been suggested for use as positive photoresists in the fabrication of electronic devices. (See Miller, R. D. et al, Materials for Microlithography: Radiation Sensitive Polymers, American Chemical Society, Washington, D.C. 1984.) In such fabrication the resist is coated on the substrate, exposed to electromagnetic radiation in the desired pattern, and delineated with a solvent that removes selectively the irradiated portions.
A small number of polysilanes containing at least a few silicon atoms bound to three other silicon atoms have also been investigated. Materials in this class have been described West and Indrikson in Journal of the American Chemical Society, 94, 6110 (1972). A combination of methyltrichlorosilane and dimethyldichlorosilane is reduced using either sodium, potassium or mixtures of sodium and potassium in a tetrahydrofuran (THF) solvent. The resulting product includes bicyclic and tricyclic silicon ring compounds plus other poorly soluble, unidentified polymeric material, for which no application was suggested. Since the formation of articles such as optical or electronic devices relies on the deposition of the fabrication materials through processes such as solvation and spin coating, the insoluble materials of West and Indrikson are not of particular advantage.
Seyferth and Yu in Design of New Materials, D. L. Cocke and A. Clearfield Eds., Plenum Publishing, 1986, have reported related material approximately represented by [MeH.sub.x Si].sub.n in which x is about 0.40. Their synthesis involves a reduction with potassium in THF of methylhydrodichlorosilane. The resulting product is characterized by the presence of one methyl group, bound hydrogen, and silicon bonds where approximately 60% of the silicon atoms are bound to three other silicon atoms. The resulting materials, like those reported by West and Indrikson, were essentially insoluble and thus again are not particularly desirable for device fabrication.
Devices such as solar cells have been produced from materials typically referred to as amorphous silicon. these materials include a high percentage of hydrogen and generally have up to 35 percent of the siliconatoms bound to three other silicon atoms. Amorphous silicon has been used successfully as a semiconductor material in devices such as solar cells. However, the material is generally deposited from the gas phase, and is extremely insoluble. It also absorbs strongly across the visible spectrum, making it unsuitable for use in some applications, e.g. waveguide applications. Thus, although interest and investigation have been intense concerning devices formed with materials having Si--Si bonds, the materials used typically have limited application.